Previous work in our Branch and elsewhere has shown that, in some individuals, psychosis is accompanied by significant elevations in the amount of phenylethylamine (PEA) excreted in the urine. PEA is a metabolite of phenylalanine and is normally produced in both the peripheral and central nervous systems. It is rapidly degraded by monoamine oxidase. PEA is known to have many behavioral similarities to amphetamines when injected into rats. In a few individuals with psychosis and elevated urinary PEA, the administration of carbidopa (an L-aromatic amino acid decarboxylase inhibitor) reduces excreted PEA and ameliorates the psychosis. We identify patients with elevated PEA by screening their urine, and then ask them to participate in a protocol comparing the effects of carbidopa and neuroleptics in a double-blind fashion. The study has been approved by the IRS. Over 90 patients have been screened, but only two people were found to have elevated urinary PEA. Unfortunately, both refused to participate in the study. The protocol has been modified to allow patients from Chestnut Lodge Hospital to participate in screening and treatment. To date, no other patients with elevated PEA have been identified.